As an example of a conventional semiconductor light-emitting device having a ridge stripe structure, a ridge waveguide semiconductor is fabricated. This semiconductor light-emitting device generally has a double heterostructure in which an active layer is provided between an n-type cladding layer and a p-type cladding layer, a portion of the p-type cladding layer being etched to form a ridge stripe portion (refer to patent documents 1, 2 and 3, for example).
For example, a ridge waveguide type semiconductor laser device composed of nitride is fabricated by sequentially laminating an n-type GaN layer 22, an n-type AlGaN layer 23, an active layer 24, and a p-type AlGaN layer 25 on a conductive substrate 21 as shown in FIG. 12, in which a portion of the p-type AlGaN layer 25 is etched by dry etching to form a ridge stripe portion C with a convex shape. A p-type GaN layer 26 is formed on top of the ridge stripe portion C.
The semiconductor laser device having such structure includes a ridge stripe portion C to form an optical waveguide. The ridge stripe portion C contributes to lateral light confinement and current constriction in the active layer 24. Light is confined by use of the effective refractive index difference between a region in the active layer 24 corresponding to the transverse width Wd at the bottom of the ridge stripe portion C and regions in the active layer 24 at both sides of the region corresponding to the width Wd. The effective refractive index difference is dependent on a film thickness t1 of a flat portion of the mesa-etched p-type AlGaN layer and is a factor determining the oscillation wavelength characteristics (spectral characteristics). Accordingly, it is important to precisely control the thickness t1.    Patent Document 1: Japanese Patent Application Publication No. 2002-204031    Patent Document 2: Japanese Patent Application Publication No. Hei 11-214788    Patent Document 3: Japanese Patent Application Publication No. Hei 10-256657